Being a caster druid has a lot less to do with the build side of things, and a lot more to do with just, y'know, preparing and casting powerful spells. You can keep your entire build exactly as it is now, but just tend towards spontaneous conversion on a less frequent basis. Maybe you can head into the holt warden+contemplative double dip combo, which grants access to the domain of your choice, along with the slots to use them. A big problem here is that offering serious advice along these lines could push you down paths even more broken than the one you're on now. Like, using hathran+acorn of far travel to cast spontaneously off the entire druid list, and aberration wild shape+nilshai form+enhance wild shape to do that twice every round. Such is the fate of druids, ever-burdened with awesomeness.